Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P11021 (BiP)
 2,049 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To be in a conformation that binds steroid, the hormone-binding domain of the glucocorticoid receptor (GR) must be bound to the 90 kDa heat shock protein (hsp90). Rabbit reticulocyte lysate contains a protein chaperone system that assembles the receptor into a heterocomplex with hsp90 and converts it from a non-steroid-binding to a steroid-binding form. Assembly of the GR-hsp90 heterocomplex requires hsp70, and in this work we examine the activities of four members of the hsp70 protein family in GR-hsp90 heterocomplex assembly. Rabbit reticulocyte lysate was depleted of hsp70 by passing it through a column of ATP agarose, resulting in the inactivation of its GR-hsp90 heterocomplex assembly activity. Addition of purified animal (mouse) or plant (wheat germ) hsp70 to the hsp70-depleted lysate permits assembly of a GR-hsp90 heterocomplex with a high affinity steroid binding site. However, purified hsp70 homologues from bacteria (DnaK) or the endoplasmic reticulum (BiP) do not promote heterocomplex formation, despite the fact that both DnaK and BiP bind to the GR in the assay system. When added to whole (i.e. hsp70-containing) reticulocyte lysate, DnaK and BiP inhibit GR-hsp90 heterocomplex assembly. Wheat germ lysate forms a heterocomplex between mouse GR and plant hsp90, but the addition of purified rabbit hsp70 to the wheat germ lysate does not increase the amount of receptor-wheat hsp90 complex produced, despite the fact that the rabbit hsp70 binds to the GR when it is added to the wheat chaperone system. The conclusion is that binding of hsp70 to receptors does not necessarily reflect a physiologically meaningful interaction. When native receptor heterocomplexes isolated from cytosols contain hsp70, it is likely that the hsp70-bound receptors represent a minority of receptors that have not yet proceeded fully through the receptor heterocomplex assembly process, which includes the dissociation of hsp70 after the binding of hsp90.
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PMID:Ability of various members of the hsp70 family of chaperones to promote assembly of the glucocorticoid receptor into a functional heterocomplex with hsp90. 883 60

A comparison of T-cell-mediated immune responses in trypanotolerant N'Dama and susceptible Boran cattle during primary infection with tsetse-transmitted Trypanosoma congolense was conducted to assess whether different patterns of T-cell activation occurred during trypanosome infection. Proliferation and IFN-gamma synthesis in response to trypanosome antigens and to the mitogen Con A were measured in LNC before infection and 10 and 35 days postinfection. Phenotypic analysis of LNC was also carried out. No significant differences in the in vitro proliferation of LNC to VSG, to hsp70/BiP, or to Con A were detected between the breeds. In contrast, IFN-gamma production in response to Con A was higher in Boran cattle at 35 days p.i. A reduction in the number of CD2+ and CD4+ T-cells and an increase in the percentage of B-cells, CD8+ T-cells, and gamma delta T-cells during infection in both N'Dama and Boran was revealed by cytofluorimetric analysis of lymph node cells.
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PMID:Trypanosoma congolense: a comparison of T-cell-mediated responses in lymph nodes of trypanotolerant and trypanosusceptible cattle during primary infection. 894 21

Recent advances in understanding the molecular pathogenesis of congenital hypothyroid goiter in cog/cog mice, have raised important questions concerning the maturation of thyroglobulin (the thyroid prohormone) in certain human kindreds with congenital goiter. We have now examined affected siblings from two unrelated families that synthesize an apparently normally glycosylated, > 300 kD immunoreactive thyroglobulin, yet have a reduced quantity of intraglandular thyroglobulin and that secreted into the circulation. From thyroid tissues of the four patients, light microscopic approaches demonstrated presence of intracellular thyroglobulin despite its absence in thyroid follicle lumina, while electron microscopy indicated abnormal distention of the endoplasmic reticulum (ER). We have confirmed biochemically that most intrathyroidal thyroglobulin fails to reach the (Golgi) compartment where complex carbohydrate modification takes place. Moreover, the disease in the affected patients is associated with massive induction of specific ER molecular chaperones including the hsp90 homolog, GRP94, and the hsp70 homolog, BiP. The data suggest that these patients synthesize a mutant thyroglobulin which is defective for folding/assembly, leading to a markedly reduced ability to export the protein from the ER. Thus, these kindreds suffer from a thyroid ER storage disease, a cell biological defect phenotypically indistinguishable from that found in cog/cog mice.
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PMID:Congenital hypothyroid goiter with deficient thyroglobulin. Identification of an endoplasmic reticulum storage disease with induction of molecular chaperones. 898 32

Proteins enter the secretory pathway by two general routes. In one, the complete polypeptide is made in the cytoplasm and held in an incompletely folded state by chaperoning adenosine triphosphatases (ATPases) such as hsp70. In Saccharomyces cerevisiae, fully synthesized secretory precursors engage the endoplasmic reticulum (ER) membrane by interaction with a set of Sec proteins comprising the polypeptide translocation apparatus (Sec61p, Sec62p, Sec63p, Sec71p, Sec72p). Productive interaction requires displacement of hsp70 from the precursor, a reaction that is facilitated by Ydj1p, a homologue of the Escherichia coli DnaJ protein. Both DnaJ and Ydj1p regulate chaperone activity by stimulating the ATPase activity of their respective hsp70 partners (E. coli DnaK and S. cerevisiae Ssa1p, respectively). In the ER lumen, another hsp70 chaperone, BiP, binds ATP and interacts with the ER membrane via its contact with a peptide loop of Sec63p. This loop represents yet another DnaJ homologue in that it contains a region of approximately 70 residue similarity to the 'J box', the most conserved region of the DnaJ family of proteins. In the presence of ATP, under conditions in which BiP can bind to Sec63p, the secretory precursor passes from the cytosol into the lumen through a membrane channel formed by Sec61p. A second route to the membrane pore that is used by many other secretory precursors, particularly in mammalian cells, requires that the polypeptide engage the ER membrane as the nascent chain emerges from the ribosome. Such cotranslational translocation bypasses the need for certain Sec proteins, instead utilizing an alternate set of cytosolic and membrane factors that allows the nascent chain to be inserted directly into the Sec61p channel.
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PMID:Polypeptide translocation machinery of the yeast endoplasmic reticulum. 898 44

The translocation of a secretory precursor protein across the ER membrane comprises three phases: docking of the precursor at the membrane, insertion into the translocation pore, and exit from the pore into the ER lumen. We demonstrate that Sec62p, Sec71p and Sec72p form a translocon subcomplex that engages secretory precursors at the membrane site of the ER translocation machinery. Binding of a precursor to the subcomplex depends on the presence of an intact signal sequence and occurs only in the absence of ATP. In the presence of ATP, the precursor is released from the subcomplex in a reaction mediated by the lumenal hsp70, BiP. This release reaction, which is specific to BiP and requires interaction between BiP and the DnaJ homolog Sec63p, defines a role for BiP and Sec63p early in the ER translocation process.
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PMID:Binding of secretory precursor polypeptides to a translocon subcomplex is regulated by BiP. 901 9

Keratin polypeptides 8 and 18 (K8/18) are intermediate filament proteins that are expressed in 'simple-type' epithelial cells. They associate with several proteins including the 70 kDa cytoplasmic heat shock proteins (hsp70). We identified the human 78 kDa glucose-regulated protein (grp78) as a keratin-associated protein. Keratin-grp78 association was noted after co-immunoprecipitation of K8/18 from HT29 detergent solubilized cell lysates, and appears to involve non-posttranslationally modified grp78. The grp78-K8/18 association is induced by culturing cells in the presence of tunicamycin or after glucose starvation. K8/18-bound grp78 can be dissociated by Mg-ATP and the association can be reconstituted in vitro using purified grp78, then redissociated again by Mg-ATP. Binding of grp78 occurs preferentially with K8, and when reconstituted does not depend on the posttranslational modification state of K8/18. Co-incubation of K8/18 with hsp70 and grp78 shows preferential association with hsp70. Our results demonstrate a direct association of grp78 with K8 under conditions that induce grp78 expression.
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PMID:Association of glucose-regulated protein (grp78) with human keratin 8. 940 41

To examine how binding of BiP (a molecular chaperone of the hsp70 family that resides in the endoplasmic reticulum) influences the conformational maturation of thyroglobulin (Tg, the precursor for thyroid hormone synthesis), we have developed a system of recombinant Tg stably expressed in wild-type Chinese hamster ovary (CHO) cells and CHO-B cells genetically manipulated for selectively increased BiP expression. The elevation of immunoreactive BiP in CHO-B cells is comparable to that seen during the unfolded protein response in the thyrocytes of certain human patients and animals suffering from congenital hypothyroid goiter with defective Tg. However, in CHO-B cells, we expressed Tg containing no mutations that induce misfolding (i.e. no unfolded protein response), so that levels of all other endoplasmic reticulum chaperones were normal. Increased availability of BiP did not accelerate Tg secretion; rather, the export of newly synthesized Tg was delayed. Tg detained intracellularly was concentrated in the endoplasmic reticulum. By coimmunoprecipitation, BiP exhibited enhanced binding to Tg in CHO-B cells. Moreover, two-dimensional gel analysis showed that BiP associated especially well with intracellular Tg containing mispaired disulfide bonds, thought to represent early Tg folding intermediates. An endoplasmic reticulum chaperone of the hsp90 family, GRP94, was also associated in Tg-chaperone complexes. The results suggest that increased binding of BiP to Tg leads to its delayed conformational maturation in the endoplasmic reticulum.
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PMID:Enhanced binding to the molecular chaperone BiP slows thyroglobulin export from the endoplasmic reticulum. 951 62

To determine whether mitochondrial hsp70 (mHsp70) could substitute for the endoplasmic retuculum (ER) Hsp70 (BiP) during protein translocation, we assembled ER-derived reconstituted proteoliposomes supplemented with either protein. We found that only BiP restored translocation in kar2 mutant vesicles and stimulated translocation approximately 3-fold in wild type proteoliposomes. mHsp70 associated poorly with both a BiP binding (DnaJ) domain of Sec63p and an ER precursor, and its ATPase activity was poorly enhanced upon incubation with the DnaJ domain. In contrast, BiP bound to the Sec63p-DnaJ domain in an ATP-dependent manner and its ATPase activity was stimulated significantly by this polypeptide. We conclude that mHsp70 is unable to support protein translocation into the ER because it fails to associate productively with Sec63p and a precursor.
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PMID:Mitochondrial Hsp70 cannot replace BiP in driving protein translocation into the yeast endoplasmic reticulum. 976 4

Immunoglobulin heavy chain-binding protein (BiP) is a member of the hsp70 family of chaperones and one of the most abundant proteins in the ER lumen. It is known to interact transiently with many nascent proteins as they enter the ER and more stably with protein subunits produced in stoichiometric excess or with mutant proteins. However, there also exists a large number of secretory pathway proteins that do not apparently interact with BiP. To begin to understand what controls the likelihood that a nascent protein entering the ER will associate with BiP, we have examined the in vivo folding of a murine lambdaI immunoglobulin (Ig) light chain (LC). This LC is composed of two Ig domains that can fold independent of the other and that each possess multiple potential BiP-binding sequences. To detect BiP binding to the LC during folding, we used BiP ATPase mutants, which bind irreversibly to proteins, as "kinetic traps." Although both the wild-type and mutant BiP clearly associated with the unoxidized variable region domain, we were unable to detect binding of either BiP protein to the constant region domain. A combination of in vivo and in vitro folding studies revealed that the constant domain folds rapidly and stably even in the absence of an intradomain disulfide bond. Thus, the simple presence of a BiP-binding site on a nascent chain does not ensure that BiP will bind and play a role in its folding. Instead, it appears that the rate and stability of protein folding determines whether or not a particular site is recognized, with BiP preferentially binding to proteins that fold slowly or somewhat unstably.
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PMID:The in vivo association of BiP with newly synthesized proteins is dependent on the rate and stability of folding and not simply on the presence of sequences that can bind to BiP. 988 41

The secretion of heterologous IgG proteins in the baculovirus-insect cell expression system is accompanied by substantial insoluble immunoglobulin in the infected cells. The accumulation of these insoluble forms suggests a limitation in the processing and secretory pathway of the infected cells. As a result, cytosolic hsp70 chaperones, which are known to associate and prevent aggregation of polypeptides in vitro, have been coexpressed in the infected cells. The hsp70 protein coprecipitated with the immunoglobulin to indicate the formation of a specific hsp70-immunoglobulin complex in vivo. Immunoblot and pulse chase studies indicated that coexpression of hsp70 increased intracellular immunoglobulin solubility. Metabolic labeling experiments revealed that hsp70 increased secreted immunoglobulin levels after several days infection as compared to infection with control baculoviruses. Pulse chase studies indicated that hsp70 increases the solubility of immunoglobulin precursors that are then processed and assembled into the complete antibody oligomer. A comparison of the action of cytosolic hsp70 chaperone to the endoplasmic reticulum chaperone BiP suggests sequential action in which hsp70 increases the solubility of preprocessed immunoglobulin, while BiP enhances the solubility of processed immunoglobulin chains.
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PMID:Overexpression of a cytosolic chaperone to improve solubility and secretion of a recombinant IgG protein in insect cells. 1019 90


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